Our long range goal is to improve the treatment of those conditions in which nasal airway impairment is believed to be a factor. The origins of this grant stem from a long standing orthodontic controversy. Whether impaired nasal respiration contributes to the development and the severity of specific elements of malocclusion, and if so, to what extent, is still unresolved. Without objective criteria to differentiate between 'normal' and 'impaired' nasal breathing, clinical decisions are based on subjective judgements. Such diagnostic imprecision renders some clinical care speculative, and lacking definable 'gold standards', precludes the qualitative evaluation of clinical decisions, and their consequences. This uncertainty continues to affect the practice of orthodontics, oral surgery and also otorhinolaryngology and allergy, in medicine. Since 1982, this grant has been highly productive, resulting in: (i) the development of a direct method for measuring oral and nasal breathing simultaneously, thus reliably determining 'respiratory mode'; (ii) determining interrelations between respiratory mode and other variables of nasal airway form and function; (iii) derivation of age and gender specific standards for children and young adults for nasorespiratory parameters; (iv) the quantification of nasorespiratory effects of some orthodontic and orthognathic procedures, and (v) testing the diagnostic utility of various tests recommended for impaired nasal breathing. Conceptually, our previous work suggests that (a) at least beyond the teen years, dentofacial morphologic variations or their therapeutic modifications do not result in significant, or predictable nasorespiratory adaptations; (b) the values and frequency distribution characteristics of nasorespiratory parameters exhibit age and gender related changes which need to be considered in clinical assessments of 'abnormality', and that (c) the mechanism for regulation of oro-nasal airflow during respiration cannot be completely, and therefore adequately, explained by variations in nasal resistance as previously believed. These findings logically lead us to the aims of the present proposal, which address the following questions: 1. Does impaired nasal breathing at younger ages, contribute to the development, or severity, of malocclusion traits ascribed to 'mouthbreathing', and if so to what extent? 2. Are age and gender related changes in nasorespiratory parameters not only predictable physiological correlates of growth and development, but also features of normal aging? 3. To what extent does respiratory mode resist switching to more oral breathing, and what are some of the adaptive responses to resistive nasal breathing? Such information should help to elucidate the control mechanisms for regulating respiratory mode, and so contribute to a better understanding of the role of abnormal upper airway function and disease.